Find and assign values in matrix

for n = 1:40 % loop over nodes with load
    triNodes = qTop(n,:);  % nodes of the considered triangle
    triDof = globDof(triNodes,:)';  % degrees of freedom in global system
    triCoord = nodeCoord(triNodes,1:nDim)  % coordinates of triangle nodes
    triCross(n,:) = cross((triCoord(1,:))-(triCoord(2,:)),(triCoord(1,:))-(triCoord(3,:)));
    triAre(n,:) = (norm(triCross(n,:))/2) ;
    q3(n,:)=[qTop(n,1) qTop(n,2) qTop(n,3) triAre(n,:)]
end 
 

I have this code which produces the following output:

q3 =
    1.0000    2.0000   90.0000    4.9424
    2.0000    3.0000   91.0000    4.3018
    3.0000    4.0000   92.0000    3.7912
    4.0000    5.0000   93.0000    3.4618
    5.0000    6.0000   94.0000    3.3465
    6.0000    7.0000   95.0000    3.4566
    7.0000    8.0000   96.0000    3.7815
    8.0000    9.0000   97.0000    4.2892
    9.0000   10.0000   98.0000    4.9293
   10.0000   11.0000   99.0000    5.6382
    ...

Now i would lige to assign 1/3 of the value in the 4th column to each of the nodenumbers in the 1st, 2nd and 3rd column.

Thereafter i would like the sum of all values assigned to eachnode to be displayed besides the node in a 10x2 matrix.

Hope you can help, thanks in advance :)

[dpb]

Not sure follow, but try

q3(:,1:3)=q3(:,1:3)+repmat(q3(:,4)/3,1,3);

or some variation on a theme depending upon what it is you really intend.

[Simon Kibsgaard]

Sorry, I can get that to work as intended.

The numbers is column 1, 2 and 3 are the numbers of my nodes. Each row is the nodes of a triangle and the area of that triangle.

Now need the area of each triangle to be divided out onto each node of that triangle. At last i need all of the areas that are divided onto node number 1 to be sumed up and so forth for each node.

[dpb]

Illustrate, don't just talk... :)

Give us the expected output from the above input.

[Simon Kibsgaard]

Of course

I'd like the output to be like this:

    1.0000    (4.9424/3)
    2.0000    (4.9424/3)+(4.3018/3)
    3.0000    (4.3018/3)+(3.7912/3)
    4.0000    (3.7912/3)+(3.4618/3)
    5.0000    (3.4618/3)+(3.3465/3)
    6.0000    (3.3465/3)+(3.4566/3)
    ... 
    98.0000   (4.9293/3)
    99.0000   (5.6382/3)
    

My dataset is much bigger than these 10 lines, otherwise it could have been done by hand.

Thanks for the help, it is very appereciated

Answer 1

[Anmol Dhiman]

Hi Simon,

Assuming your result stored in output (variable). follow the below code

areaIndex = output(:,4)/3;
finalOutput = zeros(100,2) % assuming number of nodes is 100
for i = 1:100
    idx1 = find(output(:,1)==i);
    idx2 = find(output(:,2)==i);
    idx3 = find(output(:,3)==i);
    sumArea = areaIndex(idx1) + areaIndex(idx2) + areaIndex(idx3);
    finalOutput = [i sumArea];
end

Hope it helps,

Anmol Dhiman